1. Field of the Invention
The present invention relates to a plasma processing method and a plasma processing apparatus which process a substrate using plasma.
2. Description of Related Art
Ion implantation (plasma doping) by plasma will be simply described as an example of plasma processing.
Generally, an ion implanting apparatus using plasma includes a vacuum container, a plasma generator which generates plasma within the vacuum container, a substrate holder on which a substrate is loaded within the vacuum container, a biasing power source (low frequency or pulse) which applies bias potential via the substrate holder, a vacuum pumping system (vacuum pump), and a processing gas supply system which supplies processing gas into the vacuum container.
The vacuum container is brought into a vacuum state by the vacuum pumping system. Thereafter, plasma is generated within the vacuum container by the plasma generator, processing gas is introduced into the vacuum container, a bias voltage is applied to the substrate holder, which has been loaded with the substrate, by a bias power source, and implantation of ions to the substrate is performed (for example, refer to Pamphlet of International Publication No. 2006/107044).
Meanwhile, when the inside of the vacuum container facing the plasma is clean, since substances ionized by the plasma are deposited on the inner wall of the vacuum container, it is considered that there is no emission of substances from the inner wall. However, as processing is repeated, substances to be processed are deposited on the inner wall, and are eventually emitted to the inside of the vacuum container by sputtering and evaporation. Since the emitted substances are again made into plasma in the plasma, the plasma density near the inner wall decreases as a consequence.
The results of plasma measurement are shown in FIG. 4. It can be seen that, as the number of steps increases, the plasma density near the inner wall of the vacuum container apart from the substrate center decreases. Since the distribution of ions which are deposited on and implanted into a substrate to be processed depends on the distribution of plasma, the heterogeneity of plasma distribution causes degradation of the homogeneity and repeatability of doping to the substrate.